1. Field of the Invention
The present invention relates to an apparatus and method for processing multilevel image data used in recording an image using a recording head having an overlapping part in which a plurality of chips each having a plurality of nozzle arrays overlap each other in a direction crossing a direction in which the nozzle arrays are arranged, and more particularly to such an apparatus and a method for processing multilevel image data associated with the overlapping part.
2. Description of the Related Art
It is known to configure a recording apparatus to include a recording head, of a type called a multichip recording head, having a plurality of chips each including a plurality of nozzle arrays arranged in a zig-zap fashion. One type of recording apparatus using a multichip recording head is a serial recording apparatus in which the recording head is scanned in a direction crossing a direction in which recording elements are arranged while recording paper (a recording medium) is conveyed in the same direction as the direction in which the recording elements are arranged. Another type is a full line recording apparatus in which a recording head having nozzles (discharge ports) arranged over a length corresponding to a full recording width of recording paper is fixed, while the recording paper is conveyed in a direction perpendicular to the direction in which recording elements are arranged. In the full line recording apparatus, use of the recording head having nozzles (discharge ports) arranged over the length corresponding to the full recording width of recording paper (recording medium) makes it possible to continuously record an image with the width corresponding to the full recording width of the recording paper while conveying the recording paper, and thus high-speed recording is achieved.
However, the multichip recording head has some difficulties as described below. The multichip recording head has an overlapping part in which a plurality of chips overlap each other in a direction crossing the direction in which nozzles are arranged. In this overlapping part, chip-to-chip registration errors (errors in relative positions between dots) can occur due to various factors. The registration errors can cause unevenness in color density or unevenness in the form of grains in the overlapping part, which leads to degradation in image quality. Specific examples of factors that cause of the chip-to-chip registration error are a positioning error of chips in an assembling process, a conveying error of a recording medium, etc.
Japanese Patent Laid-Open No. 5-57965 discloses a method of reducing image defects in the form of streaks in the overlapping part of the multichip recording head by complimentarily increasing or decreasing a recording duty for respective chips in the overlapping part using a mask (hereinafter, the mask for this purpose will be referred to as a gradation mask).
Japanese Patent Laid-Open No. 2000-103088 discloses a technique of compensating for a registration error by converting image data so as to enhance “robustness” to a registration error between paths in a multipath recording process. Note that “robustness” refers to resistance against density evenness caused by various errors. According to the description of Japanese Patent Laid-Open No. 2000-103088, a change in image density can occur depending on various recording conditions. In particular, a change in image density can occur when there is a perfect complementary relationship between two pieces of image data corresponding to different recording scanning paths. Japanese Patent Laid-Open No. 2000-103088 discloses a technique to produce image data corresponding to different recording scanning paths such that there is less complementary relationship thereby achieving a high “robustness” in the multipath recording process.
More specifically, in the technique disclosed in Japanese Patent Laid-Open No. 2000-103088, multilevel image data is divided into a plurality of pieces of multilevel data for a plurality of planes before binarization is performed, and the plurality of pieces of divided multilevel data are independently binarized. This makes it possible to prevent a significant change in image density from occurring even when there is a shift in recording locations of image data between different recording scanning paths. As for supplementary explanation, in a case where original image data is divided in a plurality of pieces of image data corresponding to a plurality of recording scanning paths or a plurality of nozzle arrays, the original image data can be regarded as superposition of the plurality of pieces of image data produced via the dividing. In this situation, each piece of image data can be regarded as being in one plane. In the technique disclosed in Japanese Patent Laid-Open No. 2000-103088, one recording scanning path corresponds to one plane.